Heat Pumps – How Well Do They Work?

15 responses

  1. Bob Mayer
    January 21, 2014

    I I read some of your responses on heat pump on their operation in cold weather. but I have another question. Is there a temperature below which it makes to just turn off the heat pump and use the supplemental heat system. As I sit here, it is about 12 degrees and the Supplemental light heat is on a significant amount of time. It seems to do all of the work. Note that above 20 degrees or so, the supplemental heat never turns on.
    Thank you

  2. Skip Harper
    June 11, 2014

    Being Canadian , I require HP rated for a - 20+ C .have had salesmen tell me their HP'S are rated @ -15 C but do not shut off until -25 C .I'm confused , as I have talked to owners who explained their HP's were rated @ -20 C but were useless last winter.(they used Infrared Heaters instead) Hopefully someone can explain it to me correctly.

  3. tiger2103hotmail.com
    January 11, 2016

    I did a test where I ran my heat pump/aux at 20 degrees vs emergency heat (solely the electric furnace). The heat pump, despite its nearly constant running used much less electricity per hour than the furnace which only ran 2 minutes at a time and shut off for 8 minutes.

  4. Mika Hakkinen
    November 14, 2016

    My heat pump is simply useless below 40°F. As far as I'm concerned it's a scam when they're installed anywhere but extremely temperate zones. They make a high profit for the installers, not least because since they run 24/7 they need to be replaced every few years. When you add this fact to their general ineffectiveness you can see that they're not a very good choice for those of us who don't live in Florida.

  5. Jerry
    January 11, 2017

    I would make several observations about this article on heat pumps. Heat pumps do NOT stop working at 37F, what actually happens is the efficiency starts dropping from around 3 to 4 BTU for each BTU of electricity to around 1 to 1 as the temperatures approach 0F. Also not all installations have electric resistance auxiliary heat, my home installation has a propane furnace as aux heat, the system we had installed at our last Habitat house has natural gas as aux heat. In my case I have the aux heat essentially turned off as my HP is able to maintain a comfortable temp down to -5F which is as low as it ever gets in Northern Virginia. I operate without the aux heat as a BTU heat from the HP even at 0f is still less expensive than a BTU from the propane aux heat. With natural gas a BTU from gas is roughly the same as a BTU from the HP when it is operating at 1 to 1 which is the efficiency as the temp drops below 0f.

    As to SEER ratings, in today's market, mini split HP systems can be purchased with SEER ratings in excess of 30, which is likely what we will install in our next Habitat house.

  6. Jim
    January 11, 2017

    Not sure when this article was first written, but the third paragraph of your response seems dated and prejudicial for cold climate folks.

    I live in Cincinnati, OH on a street with no option for natural gas. House is a 1800 ft^2 ranch built in 1976. My old heat pump (installed circa 1993) would not require Aux heat until the temperature dropped below 20F.

    In 2012, I replaced this unit with a near top of the line dual stage unit with a variable speed blower. There is no noticeable difference in the operation of this unit when outdoor temperatures are above 20F. It may cycle a bit more frequently, but the blower only runs at max of 80%.

    This week, we had temps down in the single digits. I never saw the Aux heat light kick on, but it was noticeable that the blower ran at 100% when temps dropped below about 12F.

    • Tim Carter
      January 11, 2017

      The original article was written in the late 1990's. The physics of how heat pumps work has not changed. The balance point may have shifted a tiny bit because of new engineering and better refrigerants, but when things like that happen, the comments here below the column get FLOODED by HVAC engineers and technicians. They provide a valuable service by helping to keep the content up-to-date.

      To date, I've not seen comments like this from them. That tells me the technical information in the above column is still rock solid and accurate.

      Rest assured that as the temperature drops outside your home and it gets farther and farther below the balance point, you're using more and more direct resistance heat inside your air handler. All you have to do is use a FLIR, or similar, infrared camera to see how orange or red your air handler is glowing! That's the giant *toaster* coils in your air handler keeping you and your family warm!

  7. Richard Preston
    January 11, 2017

    I’ve had 3 all electric homes, we build a new home about every 5 years on 5 acre rural lots outside town, so there is no gas service available and I like the simplicity and initial savings of going all electric, I could get a propane tank, but I’ve never done that. Of course the worst part of all electric is the electric back-up heat.

    In my experience here in SE Kansas, we only run into the back-up heat issue in December and January, usually only 10 or 20 days for the whole year. But when we do it is massive, like 200KWH per day instead of 75 or 80 KWH per day. It’s ridiculous. They put in 2 10KW heat strips for my houses (2000 sf upstairs, finished basement), so 20KW is a lot IMO, I toyed with only putting in one strip but the HVAC contractor said that was a bad idea. To tell the truth I’ve toyed with the idea of disconnecting the back-up heat strips and just deal with the cold for the few days.

    In the end I still pay less than if I had propane backup heat, when you figure in the initial cost, etc.

    Everything was fine on home 1, but on home 2, four years in the heat pump compressor leaked out the refrigerant, it was an inexpensive capillary tube. Didn’t realize this, and ran back-up heat all month and got a $700 electric bill. Got tube fixed and got “reamed” no pun intended, it was a Rheem unit, on the Freon because it was in 2008 and the old stock of R whatever was running low so it cost $600 dollars for the Freon load, the original HVAC contractor wanted $1000 for the freon. Well then the compressor failed and labor wasn’t covered, and even the indoor coil was leaking, turns out it was builder grade unit R13 Rheem and didn’t have low pressure compressor protection.

    So on house 3 I upgraded, didn’t get a builder unit, got a lennox xp17 (r16 for the 5ton unit). It has the low pressure compressor protection.

    TWO THINGS I LEARNED…..
    1. Shop HVAC contractors because most charge way more to install the higher efficiency unit, not just the higher equipment cost, they charge more labor too….really makes the payoff questionable. I finally found a contractor who didn’t do that
    2. HVAC installation is very important, not just the equipment quality, but a quality install is very important, duct layout and all that.

    One thing I’m still on the fence on is most of my neighbors have two smaller systems instead of one large, I’ve run into needing a 5 ton unit, and my HVAC contractor tried to talk me into going with two smaller compressors, I didn’t do it, it was $4000 more and I estimate only a couple hundred dollars a year savings if that much. I’m only spending $200 per month avg on electric. I’m all electric, and it’s 3700 sf. So that’s pretty good (our electric rates have skyrocketed last 10 years too). But I’m very energy conscious, I air dry my cloths, etc.

  8. Edward
    January 11, 2017

    I am finding that the energy auditors are teamed up with heating contractors in our area (Boston) and they are pushing "mini-splits" which are downsized heat pumps for supplementary heating, so you still need your current heating system. I question the validity of the idea since supplementary heating gets used during power outages. One of these would need a hefty backup generator.
    I am thinking of a pellet stove instead, They appear to have some kind of igniter and a blower fan. Would this work with a generator?

    Are heat pumps practical in New England climate? They would make sense in southern areas, but 37F is downright balmy for NE.

    • Rich Futyma
      January 15, 2017

      Almost a year ago, we moved into our new, super-insulated (R40 walls, R60 ceiling), 1500 sq. ft. house in upstate New York (Saratoga County). It is heated by two Mitsubishi mini-split heat pump units. They have kept us warm on a number of below-zero days, including one minus 14 degree F morning last February. We keep the temperature at 68 degrees, and don't turn it down at night. Our total electric consumption for that month was 1040 kWh, the highest so far. We thought of installing a wood stove for backup heat in case of a power outage, but opted for a whole-house generator, which cost only a little more than the wood stove would have. The mini-splits also worked great as air conditioning during the summer.

  9. Eric Coloney
    January 11, 2017

    I did a dual fuel heat pump in mid-Georgia using natural gas in 2001. Never again. Too complex and apparently requires more training and expertise than most service people can handle. It was easily a year before it was working correctly with many service visits. Additionally, the 10-10-10 year warranty required a maintenance contract that cost darn near as much as a new unit.

    I also opted for a larger unit for my upstairs than I originally had (have two units) but it still comes on at 9 am in the summertime and often runs nearly 12-13 hours and barely shuts off during that time.

    I'm not knocking a heat pump - I'm saying I wouldn't do the DUAL FUEL version again and not the brand I purchased.

    • Tim Carter
      January 11, 2017

      It sounds like the installer goofed up on his heat-gain calculations because the unit should not have to run continuously to keep the upper floors cool. What a darn shame.

    • Mike
      January 12, 2017

      You might check your ductwork to make sure that it's not leaking. We sold a house that seemed to have issues with upstairs cooling and the buyer's inspector found an 18" slice in one of our ducts. We had been air conditioning our attic! At minimum, you might have some old loose or cracked mastic that is allowing leakage, reducing the amount of cool air being delivered and making the unit run more to keep up. Hope this helps!

      • Chuck M.
        January 12, 2017

        In spite of my effusive review below of our geothermal HVAC system I had to jump on this and add that I've spent hours, and hours fixing the joke of a ductwork job done on our place. What I've discovered could've easily been done better by a Middle School shop class. Based on this and past experience with HVAC contractors I have little reason to trust the trade in general. You can pick up an endoscope on Amazon for under US$20 that you can USB into a laptop that will let you look inside your ductwork which I highly recommend.

  10. Chuck M.
    January 12, 2017

    While this is a pretty good overview of the "traditional" heat pump, as is typical of Tim, it falls short in not mentioning another use for a heat pump; in a geothermal system. We're now in our 6th year on ours in Upstate NY at 1000' elevation and we are thoroughly pleased with our decision. It does have the dreaded auxiliary resistive heating but I have not seen it come on yet (unless I test it).
    It's a bit of a misnomer to call it "geothermal" and could be closer to being a "solar" system in that we don't have thermal springs here or any volcanic activity creating heat in the ground. The heat energy in the ground we use is close enough to the surface that it's sun-warmed.

    Anyway, what we do have is a 2400sf excavation to around 6' depth and 3 loops of Pex-type flexible tube laid out on the bottom which connect to a manifold inside the house foundation. There they combine to a single loop that circulates through a Climatemaster 3 ton heatpump where heat energy is either transferred into the fan coil or removed from it and sent back out to ground for air conditioning. This is exactly how the air-source heatpump others here are talking about works (in fact we retained the fan coil when we dumped the existing air-source unit that came with the house) except that we utilize a more consistently tempered energy source since ground temps don't vary more than a few degrees throughout the year.

    The lifestyle adjustment we made for it amounts to trying to avoid large temperature swings in the house. If we need to raise the interior temps 3-4 degrees it will take 20-30 minutes, likewise if we want to lower with the AC. But again, I've yet to see the operating mode move out of Stage 2 to the AUX mode. And this whole business makes no more noise than a refrigerator, in the basement.

    This is an all electric house, 2400SF and pretty well insulated and based on usage records left to me by the former owner our overall usage is down roughly 20%-25% since we've been here. Further, our usage charges have been far more stable than if we depended on fossil fuel (I know, 'where do you think your electric comes from'. Well, it comes from a variety of sources including significant percentages of hydro and wind).

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